This invention relates to an improved process for applying aqueous coating compositions and in particular to an improved process for the application of thermosetting acrylic enamel coating compositions to provide finishes having a uniform appearance.
Thermosetting acrylic enamels are well known in the art as shown by Fraizer et al., U.S. Pat. No. 2,681,897, issued June 22, 1954; Vasta, U.S. Pat. No. 3,338,860, issued Aug. 29, 1967; Fisk et al., U.S. Pat. No. 3,365,414, issued Jan. 23, 1968; Vasta, U.S. Pat. No. 3,622,651, issued Nov. 23, 1971; Parker, U.S. Pat. No. 3,637,546, issued Jan. 25, 1972. These enamels are solvent based systems and the spray application of these enamels has not posed a problem. However, aqueous based acrylic enamels as illustrated by Taft, U.S. Pat. No. 3,661,827, issued May 9, 1972, Provide problems in drying of the finish during and after application. If the application is on a very humid day, the paint does not dry and runs and sags, and conversely, on very hot, dry days, the paint dries excessively as it is sprayed onto the panel, thereby giving a poor appearance. Also, variations in the humidity which do not cause difficulties in drying cause changes in the appearance of the paint film. In particular, paints containing metallic flakes, such as aluminum flakes, the appearance changes substantially under varying humidity conditions.
The improved process of this invention provides for initial drying conditions in which the air is under controlled temperature and humidity conditions which results in finishes that consistently have an excellent and uniform appearance without using conventional air conditioning, i.e., cooling of the air to reduce temperature and humidity.